We plan to develop a novel synthetic vector, which includes several key features that favor in vivo gene delivery to the liver. This type of non-viral vector consists of a new design of bifunctional compounds that contain a terminal polyamine group as the DNA binding segment, terminal galactose residues as the target binding segment and an aliphatic linker to bridge the two functional groups together. When mixed with DNA, the DNA binding segment of the bifunctional compounds binds DNA through electrostatic interaction, allowing the formation of a neutral complex in which the DNA molecule is coated with a sheath of bifunctional molecules and the galactose residues exposed on the surface. As DNA is wrapped inside, it is protected against enzyme degradation in extracellular fluid as it travels from the site of injection to the target cells. Being small in size and bearing targeting ligands on surface, these electrostatically neutral particles will avoid nonspecific binding to non-targeted cells, the extracellular matrix and blood components. In addition the particles will be able to pass through liver fenestrae, bind to hepatocytes through asialoglycoprotein receptors and deliver transgene into hepatocytes. To achieve our goal, we will optimize the structure of each of the three segments in the bifunctional compounds with respect to their effect on DNA binding, formation of DNA complex, the stability of complexes in serum, target specific binding and gene delivery. The experimental approach includes the synthesis of structural analogues of each functional segment followed by assembling a pool of bifunctional compounds with different structural combinations. An ideal structure of bifunctional compound will then be selected using biochemical, biophysical and biological methods. The properties of target specific gene delivery of the selected bifunctional compounds will be evaluated in vitro and in vivo employing cell culture and animal models. The successful accomplishment of the proposed objective will establish new methodologies for synthesis of bifunctional compounds that will provide a novel synthetic vector for the gene therapy.